t is no more than proper that we should abide by analogy, at
least in some measure, during their development; and that analogy which
suggests the revolution, suggests at the same time a central orb about
which it should be performed:--so far the astronomer was consistent. This
central orb, however, should, dynamically, be greater than all the orbs,
taken together, which surround it. Of these there are about 100
millions. "Why, then," it was of course demanded, "do we not _see_ this
vast central sun--_at least equal_ in mass to 100 millions of such suns
as ours--why do we not _see_ it--_we_, especially, who occupy the mid
region of the cluster--the very locality _near_ which, at all events,
must be situated this incomparable star?" The reply was ready--"It must
be non-luminous, as are our planets." Here, then, to suit a purpose,
analogy is suddenly let fall. "Not so," it may be said--"we know that
non-luminous suns actually exist." It is true that we have reason at
least for supposing so; but we have certainly no reason whatever for
supposing that the non-luminous suns in question are encircled by
_luminous_ suns, while these again are surrounded by non-luminous
planets:--and it is precisely all this with which Maedler is called upon
to find any thing analogous in the heavens--for it is precisely all this
which he imagines in the case of the Galaxy. Admitting the thing to be
so, we cannot help here picturing to ourselves how sad a puzzle the _why
it is so_ must prove to all _a priori_ philosophers.

But granting, in the very teeth of analogy and of every thing else, the
non-luminosity of the vast central orb, we may still inquire how this
orb, so enormous, could fail of being rendered visible by the flood of
light thrown upon it from the 100 millions of glorious suns glaring in
all directions about it. Upon the urging of this question, the idea of
an actually solid central sun appears, in some measure, to have been
abandoned; and speculation proceeded to assert that the systems of the
cluster perform their revolutions merely about an immaterial centre of
gravity common to all. Here again then, to suit a purpose, analogy is
let fall. The planets of our system revolve, it is true, about a common
centre of gravity; but they do this in connexion with, and in
consequence of, a material sun whose mass more than counterbalances the
rest of the system.

The mathematical circle is a curve composed of an infinity of straight
line